ERA5 almanac comparison — 8 years of real data
Big Sky vs McCall: weather in September
McCall edges out Big Sky for sun in September: 34% clear historically versus 8% (8-year ERA5 average, a 26-point gap). Both are viable — McCall is the safer bet.
What you are reading: 8-year historical averages, not a forecast.
Either destination can still surprise you this specific September. For this
week’s actual forecast, each destination links to its live page below.
Big Sky
MT
- Clear days, September
- 8%
- Sample size
- n=240 days
- Avg high
- 62°F
- Early September (1st–15th)
- 17%
- Late September (16th–end)
- 0%
McCall
ID
- Clear days, September
- 34%
- Sample size
- n=240 days
- Avg high
- 70°F
- Early September (1st–15th)
- 49%
- Late September (16th–end)
- 19%
Compare Big Sky vs McCall in another month
All percentages are historical averages from the ERA5 reanalysis via Open-Meteo, 8 full years (2018–2025). “Clear” means avg high ≥ 72 °F, precipitation < 1 mm, and a non-precipitation weather code. This is history, not a forecast. The live 7-day outlook for any destination is on its own page and may differ from the long-run average. Data from Open-Meteo.